What’s the point? This reduces the amount of data you need to download per page, which could potentially save users considerable money on metered data plans — more common outside the U.S. Or it at least speeds up Web page load times, something we could definitely use for AT&T’s often-pokey connection.

It’s probably not something that most iPhone users will bother to download. But it’s potentially useful for a subset of them, who might even pay for it.

The challenge: Before Opera can get those browsers to customers, it needs Apple’s seal of approval. Will the increasingly closed-off Apple approve this app — a competitor to its Safari browser, which generates millions of dollars in revenue per year — for the iPhone App Store?

That probably depends mostly on technical factors. It would be hard for Apple to reject an app today purely for anti-competitive reasons, unless it wants the FTC in its face. (Though it may offer the same idiotic response it offered for sitting on Google Voice, that it “appears to alter the iPhone’s distinctive user experience.”)

For Apple to approve the app technically, it must be certain that Opera is only using public programming tools (called APIs) that Apple allows iPhone developers to use, and no illegal or private APIs. That could be sketchy for a Web browser app.

Part of the developer rules state that third-party code interpreters — like Flash, or another Web browser engine — are banned. But because we don’t know the technical design of Opera Mini, we’re not sure if there’s any illicit stuff in the app itself, or whether this is all done on Opera’s servers.

Assuming the heavy lifting is done server-side, displaying Web content either using the public Mobile Safari APIs, or via a screen-sharing protocol like VNC, it’s possible that Opera Mini will be approved. (Assuming Apple is OK with Web requests going through Opera’s proxy servers, assuming they do in this app.)

An Opera rep, asked for details, did not sufficiently explain how the app works, or why it thinks Apple will approve it. (We’re still trying to get more information out of Opera.) But this rep says, “Opera Mini 5 on the iPhone is not in violation of any of the requirements as we see it.” Of course, as Opera “sees it” is meaningless. All that matters is how Apple sees it.

sceptics point out that Opera may just be demonstrating this app on the iPhone as a stunt to drum up interest in its Opera Mini browsers for other, more open platforms, such as Symbian, Windows Mobile, or Android.

But that’s silly. The iPhone App platform is a huge ecosystem of more than 75 million units, and of course Opera would like to be able to sell into it. (Opera Mini could even be useful on the iPad, if its data-reduction methods make AT&T’s $14.99 per month, 250 MB data plan more useful.)

Whether it can will depend on how well it’s been able to build Opera Mini for the iPhone, and if it’s truly within the “legal” boundaries of the App Store.